#include<bits/stdc++.h>
#define ONLINE_JUDGE
#define ll long long
#define ull unsigned long long
using namespace std;

const ll N = 1e6 + 10, INF = 0x3f3f3f3f;

ll q, l, r;

void solve()
{
    cin >> q;
    while (q--) {
        cin >> l >> r;
        if (l == r) { cout << -1 << '\n';continue; }
        ll cnt0 = r / 2 - (l - 1) / 2;
        ll cnt1 = r - l + 1 - cnt0;

        if (r - l + 1 == 2) {
            if (l == 1) cout << 0 << '\n';
            else cout << -1 << '\n';
        } else cout << abs(cnt1 - cnt0) << '\n';
    }
}

signed main()
{
    // ios::sync_with_stdio(0);
    // cin.tie(0);cout.tie(0);
#ifndef ONLINE_JUDGE
    std::istringstream in(R"()");
    std::cin.rdbuf(in.rdbuf());
#endif
    ll T = 1;
    //cin>>T;
    for (ll i = 1;i <= T;i++) {
        solve();
    }
}